SuzukiSavage.com - Print Page

SuzukiSavage.com
/cgi-bin/YaBB.pl
General Category >> Rubber Side Down! >> Engine dies above half throttle
/cgi-bin/YaBB.pl?num=1246802228

Message started by DrT on 07/05/09 at 06:57:07

Title: Engine dies above half throttle
Post by DrT on 07/05/09 at 06:57:07

I have rebuilt an old Savage that I was originally going to use for spares - I decided to put it back on the road instead. It starts easily. It idles with no problem. It runs well and pulls hard - up to about half throttle. If the throttle is opened to more than half the engine immediately dies - there may be a splutter or two if the throttle is kept wide open but the only way to resume running is to reduce throttle to below half. It then runs fine. I have checked that the main jet is clear and I have tried increasing the main jet size - makes no difference.

There is no obvious problem with the air intake on the filter side.

It exhibits the same behaviour with both normal and "prime" settings of the fuel tap.

My instinct is that this is a carb problem but I haven't ruled out electrical. It seems likely that it is either too liitle or too much fuel (or too little/too much air). It also seems likley to be main jet related as it runs so well at lower throttle openings. Any suggestions would be very welcome.

Title: Re: Engine dies above half throttle
Post by justin_o_guy2 on 07/05/09 at 09:03:11

If I thought it was electrical Id put a timing light on it & see if the plug stops firing when the engine goes to crap. That would not fix the problem, I know, but it might help you find it. Im l4eaning toward the carb, but eliminating the electrical option would make me feel better if it was my problem.

Title: Re: Engine dies above half throttle
Post by SV og LS on 07/05/09 at 09:17:27

It's not main jet size. It won't shut down altogether even if there was a 125 installed provided nothing's blocked. I'd check fuel delivery first - as a quick check yank the fuel hose off the carb and check how the fuel flows out in PRI. You don't have any aftermarket filters which might slow down the fuel flow?

Title: Re: Engine dies above half throttle
Post by Serowbot on 07/05/09 at 10:12:36

Check that the needle-jet slide is not sticking,... while you're in there you might as well clean all the fuel passages in the carb. Don't just use carb cleaner, find a very fine wire to run up and down the passages. .009 to .011" Guitar strings work great.

Title: Re: Engine dies above half throttle
Post by justin_o_guy2 on 07/05/09 at 10:13:45

I dont know if its possible for the twist grip & kill switch to get together, but if you reach down on the carb itself to throttle it up, if that makes a difference, then youll have it found.

Title: Re: Engine dies above half throttle
Post by Serowbot on 07/05/09 at 10:34:41

Keep in mind that as throttle increases, the carb circuits work cumulatively. Pilot and needle circuits don't stop when the main opens. And without the needle-jet slide working, the main is essentially blocked.

Title: Re: Engine dies above half throttle
Post by justin_o_guy2 on 07/05/09 at 10:41:38

So a stuck slide will do this?

Title: Re: Engine dies above half throttle
Post by DrT on 07/05/09 at 10:42:59

OK - I have checked the "prime" setting and the fuel flows fine. I have run it without the air filter - seems slightly better but no major difference. I have checked the electrics and the regulator is working OK.

I am starting to wonder if the coil is breaking down under load or the CDI is malfunctioning.

Title: Re: Engine dies above half throttle
Post by Yonuh Adisi on 07/05/09 at 11:08:07

Remove the top of the carb and check to be sure the spring didn't get bunched up or the diaphragm ain't damaged.

Title: Re: Engine dies above half throttle
Post by bill67 on 07/05/09 at 11:29:38

I would run some Sea Foam in it could be carb slide in sticking.

Title: Re: Engine dies above half throttle
Post by Serowbot on 07/05/09 at 12:06:04

2B343235282F1E2E1E26343873410 wrote:

So a stuck slide will do this?

It can,... the main jet screws into the bottom of the needle jet, so if the needle is stuck down, it will block some fuel flow.

Title: Re: Engine dies above half throttle
Post by justin_o_guy2 on 07/05/09 at 12:11:34

Not trying to start anything, cuz I am no kinda carb guy. They are as magical as transistors to me. So, that said.

If the slide has lifted enough to clear the main of the metering rod, would it still make it die? Is making it to 1/2 throttle enough to make a stuck slide less likely the culprit? If it was up to 1/2 throttle & rolled off just as it started to act up, would it go to idle slowly due to the slide hanging?

Title: Re: Engine dies above half throttle
Post by Serowbot on 07/05/09 at 12:35:58

Wow!,... I can't think that one out...
Now that I'm thinking about it too much, I can't figure how the vacuum opens the slide.... Seems like it would pull it closed, if drawing from below, and that's what the function of the spring is. So, it must pull from the top?...
I swear it all made sense yesterday.....
My head hurts... :-?

Main thing is,... clean everything in the carb. Oh,.. and check that the washer under the main jet is in place. That being missing would put the main further up into the needle. Might cause trouble too.

Title: Re: Engine dies above half throttle
Post by DrT on 07/05/09 at 14:11:54

OK its NOT the carb! I remembered that I had another carb in my spares box so I tried that - same problem. Then I tried a different plug - same problem. I am now 99% certain that its the coil. I have a replecement on its way (good old ebay) so I'll try that next.